Implicitly linking aperiodic channel state information (a-csi) reports to csi-reference signal (csi-rs) resources

ABSTRACT

Certain aspects of the present disclosure provide techniques for implicitly linking aperiodic channel state information (A-CSI) reports to CSI-reference signal (CSI-RS) resources. In an aspect, the UE may be instructed to report on specific CSI-RS resource(s) via explicit signaling in the UE grant. Other aspects disclose techniques for implicit CSI-RS resource selection by the UE that require fewer signaling resources. Instead of explicitly signaling CSI-RS resources to the UE, the UE may implicitly select CSI-RS resource for CSI feedback reporting based on information known to the UE, e.g. a subframe on which a reporting request is received. This may reduce the impact of the additional signaling in the UE grant.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional of U.S. patent application Ser. No.13/360,348 filed on Jan. 27, 2012, which is a continuation-in-part ofU.S. patent application Ser. No. 13/359,154 filed on Jan. 26, 2012,entitled “Feedback Reporting Based on Channel State InformationReference Signal (CSI-RS) Groups” which claims benefit of U.S.Provisional Patent Application Ser. No. 61/444,568 filed on Feb. 18,2011, entitled “Feedback Reporting Based on CSI-RS Groups,” U.S.Provisional Patent Application Ser. No. 61/444,979 filed on Feb. 21,2011, entitled “Feedback Reporting Based on CSI-RS Groups,” and U.S.Provisional Patent Application Ser. No. 61/524,034 filed on Aug. 16,2011, entitled “Feedback Reporting Based on CSI-RS Groups,” all of whichare incorporated herein by reference in their entirety for all purposes.

BACKGROUND

Field

The present disclosure relates generally to communication systems, andmore particularly, to implicitly linking aperiodic channel stateinformation (A-CSI) reports to CSI-reference signal (CSI-RS) resources.

Background

Wireless communication systems are widely deployed to provide varioustelecommunication services such as telephony, video, data, messaging,and broadcasts. Typical wireless communication systems may employmultiple-access technologies capable of supporting communication withmultiple users by sharing available system resources (e.g., bandwidth,transmit power). Examples of such multiple-access technologies includecode division multiple access (CDMA) systems, time division multipleaccess (TDMA) systems, frequency division multiple access (FDMA)systems, orthogonal frequency division multiple access (OFDMA) systems,single-carrier frequency division multiple access (SC-FDMA) systems, andtime division synchronous code division multiple access (TD-SCDMA)systems.

These multiple access technologies have been adopted in varioustelecommunication standards to provide a common protocol that enablesdifferent wireless devices to communicate on a municipal, national,regional, and even global level. An example of an emergingtelecommunication standard is Long Term Evolution (LTE). LTE is a set ofenhancements to the Universal Mobile Telecommunications System (UMTS)mobile standard promulgated by Third Generation Partnership Project(3GPP). It is designed to better support mobile broadband Internetaccess by improving spectral efficiency, lower costs, improve services,make use of new spectrum, and better integrate with other open standardsusing OFDMA on the downlink (DL), SC-FDMA on the uplink (UL), andmultiple-input multiple-output (MIMO) antenna technology. However, asthe demand for mobile broadband access continues to increase, thereexists a need for further improvements in LTE technology. Preferably,these improvements should be applicable to other multi-accesstechnologies and the telecommunication standards that employ thesetechnologies.

SUMMARY

In LTE REL-10, no ambiguity exists with respect to CSI-RS reporting asthere is only one CSI-RS configuration with non-zero power, andtherefore a UE may look at the CSI-RS configuration and report back theCSI that is aligned with the configured resource. However, it may bepossible to configure multiple non-zero power CSI-RS resources (orgroups) in LTE REL-11. Currently, the standards do not discuss how theUE may select CSI-RS resources for feedback reporting. In an aspect, theUE may be told the specific CSI-RS resource(s) it should report on byincluding explicit signaling in the UE grant. However, this may includesignificant resource impact as additional resource (e.g. bits) may needto be allocated in the UE grant for such explicit signaling. Thus, thereis a need for a technique for CSI-RS resource selection by the UE thatdoes not include a significant resource impact. In certain aspects,instead of explicitly signaling to the UE which CSI-RS resources it mayselect for CSI feedback reporting, the UE may be implicitly triggeredbased on some information the UE already possesses, e.g. which subframea reporting request was received. This may save the additional bits forsignaling the CSI-RS resources in the UE grant, thus avoiding thesignaling impact. In certain aspects, the UE may determine CSI-RSresources for feedback reporting based on a subframe in which a requestfor the feedback report was received.

Certain aspects of the present disclosure provide a method for wirelesscommunications that may be performed by a UE. The method generallyincludes receiving a request for a channel state information (CSI)feedback report, determining a set of one or more reference CSIreference signal (CSI-RS) resources for feedback reporting, at least inpart based on a time in which the request was received, generating thefeedback report based on the set of one or more reference CSI-RSresources, and transmitting the feedback report.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes a receiverconfigured to receive a request for a channel state information (CSI)feedback report, at least one processor configured to determine a set ofone or more reference CSI reference signal (CSI-RS) resources forfeedback reporting, at least in part based on a time in which therequest was received and generate the feedback report based on the setof one or more reference CSI-RS resources, and a transmitter configuredto transmit the feedback report.

Certain aspects of the present disclosure provide an apparatus forwireless communication. The apparatus generally includes means forreceiving a request for an channel state information (CSI) feedbackreport, means for determining a set of one or more reference CSIreference signal (CSI-RS) resources for feedback reporting, at least inpart based on a time in which the request was received, means forgenerating the feedback report based on the set of one or more referenceCSI-RS resources, and means for transmitting the feedback report.

Certain aspects of the present disclosure provide a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium comprising code forreceiving a request for an channel state information (CSI) feedbackreport, determining a set of one or more reference CSI reference signal(CSI-RS) resources for feedback reporting, at least in part based on atime in which the request was received, generating the feedback reportbased on the set of one or more reference CSI-RS resources, andtransmitting the feedback report.

Certain aspects of the present disclosure provide a method for wirelesscommunications that may be performed by a base station. The methodgenerally includes determining a map, the map correlating channel stateinformation reference signal (CSI-RS) resources with a CSI feedbackreport request based, at least in part, on the timing of the request,determining a set of one or more reference CSI-RS resources for feedbackreporting, transmitting a request for a CSI feedback report at a time,based at least in part on a mapping of the set of one or more referenceCSI-RS resources to the time, and receiving a feedback report based onthe set of one or more reference CSI-RS resources.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes at least oneprocessor configured to determine a map, the map correlating channelstate information reference signal (CSI-RS) resources with a CSIfeedback report request based, at least in part, on the timing of therequest, and determine a set of one or more reference CSI-RS resourcesfor feedback reporting. The apparatus further includes a transmitterconfigured to transmit a request for a CSI feedback report at a time,based at least in part on a mapping of the set of one or more referenceCSI-RS resources to the time, and a receiver configured to receive afeedback report based on the set of one or more reference CSI-RSresources.

Certain aspects of the present disclosure provide an apparatus forwireless communications. The apparatus generally includes means fordetermining a map, the map correlating channel state informationreference signal (CSI-RS) resources with a CSI feedback report requestbased, at least in part, on the timing of the request, means fordetermining a set of one or more reference CSI-RS resources for feedbackreporting, means for transmitting a request for a CSI feedback report ata time, based at least in part on a mapping of the set of one or morereference CSI-RS resources to the time, and means for receiving afeedback report based on the set of one or more reference CSI-RSresources.

Certain aspects of the present disclosure include a computer-programproduct for wireless communications. The computer-program productgenerally includes a computer-readable medium generally including codefor determining a map, the map correlating channel state informationreference signal (CSI-RS) resources with a CSI feedback report requestbased, at least in part, on the timing of the request, determining a setof one or more reference CSI-RS resources for feedback reporting,transmitting a request for a CSI feedback report at a time, based atleast in part on a mapping of the set of one or more reference CSI-RSresources to the time, and receiving a feedback report based on the setof one or more reference CSI-RS resources.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a network architecture.

FIG. 2 is a diagram illustrating an example of an access network.

FIG. 3 is a diagram illustrating an example of a DL frame structure inLTE.

FIG. 4 is a diagram illustrating an example of an UL frame structure inLTE.

FIG. 5 is a diagram illustrating an example of a radio protocolarchitecture for the user and control planes.

FIG. 6 is a diagram illustrating an example of an evolved Node B anduser equipment in an access network.

FIG. 7 is a diagram illustrating a range expanded cellular region in aheterogeneous network.

FIG. 8 is a diagram illustrating a network with a macro eNB and remoteradio heads (RRHs) in accordance with certain aspects of the presentdisclosure.

FIG. 9 is a diagram illustrating CSI-RS groups corresponding todifferent cells in accordance with certain aspects of the presentdisclosure.

FIG. 10 is a diagram illustrating CSI-RS groups in which multiplecells/TxPs form one group in accordance with certain aspects of thepresent disclosure.

FIG. 11 is a diagram illustrating predefined cycling in two dimensions,first across CSI-RS groups, then across bandwidth parts (BWPs) inaccordance with certain aspects of the present disclosure.

FIG. 12 is a diagram illustrating predefined cycling in two dimensions,first across BWPs, then across CSI-RS groups in accordance with certainaspects of the present disclosure.

FIG. 13 is a diagram illustrating example operations performed, forexample by a transmitter, in accordance with certain aspects of thepresent disclosure.

FIG. 13A illustrates example components capable of performing theoperations illustrated in FIG. 13 in accordance with certain aspects ofthe present disclosure.

FIG. 14 is a diagram illustrating example operations performed, forexample by a UE. in accordance with certain aspects of the presentdisclosure.

FIG. 14A illustrates example components capable of performing theoperations illustrated in FIG. 14 in accordance with certain aspects ofthe present disclosure.

FIG. 15 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system inaccordance with certain aspects of the present disclosure.

FIG. 16 illustrates an example configuration of three CSI-RS resourcesin a single subframe in accordance with certain aspects of the presentdisclosure.

FIG. 17 is a diagram illustrating example operations performed, forexample by a user equipment (UE), for implicit triggering CSI reportingin accordance with certain aspects of the present disclosure.

FIG. 17A illustrates example components capable of performing theoperations illustrated in FIG. 17 in accordance with certain aspects ofthe present disclosure.

FIG. 18 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system inaccordance with certain aspects of the present disclosure.

FIG. 19 illustrates example operations performed, for example, by a basestation, in accordance with certain aspects of the present disclosure.

FIG. 19A illustrates example components capable of performing theoperations illustrated in FIG. 19 in accordance with certain aspects ofthe present disclosure.

FIG. 20 is a diagram illustrating an example of a hardwareimplementation for an apparatus employing a processing system inaccordance with certain aspects of the present disclosure

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of telecommunication systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawing by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise. The software may reside ona computer-readable medium. The computer-readable medium may be anon-transitory computer-readable medium. A non-transitorycomputer-readable medium include, by way of example, a magnetic storagedevice (e.g., hard disk, floppy disk, magnetic strip), an optical disk(e.g., compact disk (CD), digital versatile disk (DVD)), a smart card, aflash memory device (e.g., card, stick, key drive), random access memory(RAM), read only memory (ROM), programmable ROM (PROM), erasable PROM(EPROM), electrically erasable PROM (EEPROM), a register, a removabledisk, and any other suitable medium for storing software and/orinstructions that may be accessed and read by a computer. Thecomputer-readable medium may be resident in the processing system,external to the processing system, or distributed across multipleentities including the processing system. The computer-readable mediummay be embodied in a computer-program product. By way of example, acomputer-program product may include a computer-readable medium inpackaging materials. Those skilled in the art will recognize how best toimplement the described functionality presented throughout thisdisclosure depending on the particular application and the overalldesign constraints imposed on the overall system.

Accordingly, in one or more exemplary embodiments, the functionsdescribed may be implemented in hardware, software, firmware, or anycombination thereof. If implemented in software, the functions may bestored on or encoded as one or more instructions or code on acomputer-readable medium. Computer-readable media includes computerstorage media. Storage media may be any available media that can beaccessed by a computer. By way of example, and not limitation, suchcomputer-readable media can comprise RAM, ROM, EEPROM, CD-ROM or otheroptical disk storage, magnetic disk storage or other magnetic storagedevices, or any other medium that can be used to carry or store desiredprogram code in the form of instructions or data structures and that canbe accessed by a computer. Disk and disc, as used herein, includescompact disc (CD), laser disc, optical disc, digital versatile disc(DVD), floppy disk and Blu-ray disc where disks usually reproduce datamagnetically, while discs reproduce data optically with lasers.Combinations of the above should also be included within the scope ofcomputer-readable media.

FIG. 1 is a diagram illustrating an LTE network architecture 100. TheLTE network architecture 100 may be referred to as an Evolved PacketSystem (EPS) 100. The EPS 100 may include one or more user equipment(UE) 102, an Evolved UMTS Terrestrial Radio Access Network (E-UTRAN)104, an Evolved Packet Core (EPC) 110, a Home Subscriber Server (HSS)120, and an Operator's IP Services 122. The EPS can interconnect withother access networks, but for simplicity those entities/interfaces arenot shown. As shown, the EPS provides packet-switched services, however,as those skilled in the art will readily appreciate, the variousconcepts presented throughout this disclosure may be extended tonetworks providing circuit-switched services.

The E-UTRAN includes the evolved Node B (eNB) 106 and other eNBs 108.The eNB 106 provides user and control plane protocol terminations towardthe UE 102. The eNB 106 may be connected to the other eNBs 108 via an X2interface (e.g., backhaul). The eNB 106 may also be referred to as abase station, a base transceiver station, a radio base station, a radiotransceiver, a transceiver function, a basic service set (BSS), anextended service set (ESS), or some other suitable terminology. The eNB106 provides an access point to the EPC 110 for a UE 102. Examples ofUEs 102 include a cellular phone, a smart phone, a session initiationprotocol (SIP) phone, a laptop, a personal digital assistant (PDA), asatellite radio, a global positioning system, a multimedia device, avideo device, a digital audio player (e.g., MP3 player), a camera, agame console, or any other similar functioning device. The UE 102 mayalso be referred to by those skilled in the art as a mobile station, asubscriber station, a mobile unit, a subscriber unit, a wireless unit, aremote unit, a mobile device, a wireless device, a wirelesscommunications device, a remote device, a mobile subscriber station, anaccess terminal, a mobile terminal, a wireless terminal, a remoteterminal, a handset, a user agent, a mobile client, a client, or someother suitable terminology.

The eNB 106 is connected by an S1 interface to the EPC 110. The EPC 110includes a Mobility Management Entity (MME) 112, other MMES 114, aServing Gateway 116, and a Packet Data Network (PDN) Gateway 118. TheMME 112 is the control node that processes the signaling between the UE102 and the EPC 110. Generally, the MME 112 provides bearer andconnection management. All user IP packets are transferred through theServing Gateway 116, which itself is connected to the PDN Gateway 118.The PDN Gateway 118 provides UE IP address allocation as well as otherfunctions. The PDN Gateway 118 is connected to the Operator's IPServices 122. The Operator's IP Services 122 may include the Internet,the Intranet, an IP Multimedia Subsystem (IMS), and a PS StreamingService (PSS).

FIG. 2 is a diagram illustrating an example of an access network 200 inan LTE network architecture. In this example, the access network 200 isdivided into a number of cellular regions (cells) 202. One or more lowerpower class eNBs 208 may have cellular regions 210 that overlap with oneor more of the cells 202. A lower power class eNB 208 may be referred toas a remote radio head (RRH). The lower power class eNB 208 may be afemto cell (e.g., home eNB (HeNB)), pico cell, or micro cell. The macroeNBs 204 are each assigned to a respective cell 202 and are configuredto provide an access point to the EPC 110 for all the UEs 206 in thecells 202. There is no centralized controller in this example of anaccess network 200, but a centralized controller may be used inalternative configurations. The eNBs 204 are responsible for all radiorelated functions including radio bearer control, admission control,mobility control, scheduling, security, and connectivity to the servinggateway 116.

The modulation and multiple access scheme employed by the access network200 may vary depending on the particular telecommunications standardbeing deployed. In LTE applications, OFDM is used on the DL and SC-FDMAis used on the UL to support both frequency division duplexing (FDD) andtime division duplexing (TDD). As those skilled in the art will readilyappreciate from the detailed description to follow, the various conceptspresented herein are well suited for LTE applications. However, theseconcepts may be readily extended to other telecommunication standardsemploying other modulation and multiple access techniques. By way ofexample, these concepts may be extended to Evolution-Data Optimized(EV-DO) or Ultra Mobile Broadband (UMB). EV-DO and UMB are air interfacestandards promulgated by the 3rd Generation Partnership Project 2(3GPP2) as part of the CDMA2000 family of standards and employs CDMA toprovide broadband Internet access to mobile stations. These concepts mayalso be extended to Universal Terrestrial Radio Access (UTRA) employingWideband-CDMA (W-CDMA) and other variants of CDMA, such as TD-SCDMA;Global System for Mobile Communications (GSM) employing TDMA; andEvolved UTRA (E-UTRA), Ultra Mobile Broadband (UMB), IEEE 802.11(Wi-Fi), IEEE 802.16 (WiMAX), IEEE 802.20, and Flash-OFDM employingOFDMA. UTRA, E-UTRA, UMTS, LTE and GSM are described in documents fromthe 3GPP organization. CDMA2000 and UMB are described in documents fromthe 3GPP2 organization. The actual wireless communication standard andthe multiple access technology employed will depend on the specificapplication and the overall design constraints imposed on the system.

The eNBs 204 may have multiple antennas supporting MIMO technology. Theuse of MIMO technology enables the eNBs 204 to exploit the spatialdomain to support spatial multiplexing, beamforming, and transmitdiversity. Spatial multiplexing may be used to transmit differentstreams of data simultaneously on the same frequency. The data steamsmay be transmitted to a single UE 206 to increase the data rate or tomultiple UEs 206 to increase the overall system capacity. This isachieved by spatially precoding each data stream (i.e., applying ascaling of an amplitude and a phase) and then transmitting eachspatially precoded stream through multiple transmit antennas on the DL.The spatially precoded data streams arrive at the UE(s) 206 withdifferent spatial signatures, which enables each of the UE(s) 206 torecover the one or more data streams destined for that UE 206. On theUL, each UE 206 transmits a spatially precoded data stream, whichenables the eNB 204 to identify the source of each spatially precodeddata stream.

Spatial multiplexing is generally used when channel conditions are good.When channel conditions are less favorable, beamforming may be used tofocus the transmission energy in one or more directions. This may beachieved by spatially precoding the data for transmission throughmultiple antennas. To achieve good coverage at the edges of the cell, asingle stream beamforming transmission may be used in combination withtransmit diversity.

In the detailed description that follows, various aspects of an accessnetwork will be described with reference to a MIMO system supportingOFDM on the DL. OFDM is a spread-spectrum technique that modulates dataover a number of subcarriers within an OFDM symbol. The subcarriers arespaced apart at precise frequencies. The spacing provides“orthogonality” that enables a receiver to recover the data from thesubcarriers. In the time domain, a guard interval (e.g., cyclic prefix)may be added to each OFDM symbol to combat inter-OFDM-symbolinterference. The UL may use SC-FDMA in the form of a DFT-spread OFDMsignal to compensate for high peak-to-average power ratio (PAPR).

FIG. 3 is a diagram 300 illustrating an example of a DL frame structurein LTE. A frame (10 ms) may be divided into 10 equally sized sub-frames.Each sub-frame may include two consecutive time slots. A resource gridmay be used to represent two time slots, each time slot including aresource block. The resource grid is divided into multiple resourceelements. In LTE, a resource block contains 12 consecutive subcarriersin the frequency domain and, for a normal cyclic prefix in each OFDMsymbol, 7 consecutive OFDM symbols in the time domain, or 84 resourceelements. For an extended cyclic prefix, a resource block contains 6consecutive OFDM symbols in the time domain and has 72 resourceelements. Some of the resource elements, as indicated as R 302, 304,include DL reference signals (DL-RS). The DL-RS include Cell-specific RS(CRS) (also sometimes called common RS) 302 and UE-specific RS (UE-RS)304. UE-RS 304 are transmitted only on the resource blocks upon whichthe corresponding physical DL shared channel (PDSCH) is mapped. Thenumber of bits carried by each resource element depends on themodulation scheme. Thus, the more resource blocks that a UE receives andthe higher the modulation scheme, the higher the data rate for the UE.

FIG. 4 is a diagram 400 illustrating an example of an UL frame structurein LTE. The available resource blocks for the UL may be partitioned intoa data section and a control section. The control section may be formedat the two edges of the system bandwidth and may have a configurablesize. The resource blocks in the control section may be assigned to UEsfor transmission of control information. The data section may includeall resource blocks not included in the control section. The UL framestructure results in the data section including contiguous subcarriers,which may allow a single UE to be assigned all of the contiguoussubcarriers in the data section.

A UE may be assigned resource blocks 410 a, 410 b in the control sectionto transmit control information to an eNB. The UE may also be assignedresource blocks 420 a, 420 b in the data section to transmit data to theeNB. The UE may transmit control information in a physical UL controlchannel (PUCCH) on the assigned resource blocks in the control section.The UE may transmit only data or both data and control information in aphysical UL shared channel (PUSCH) on the assigned resource blocks inthe data section. A UL transmission may span both slots of a subframeand may hop across frequency.

A set of resource blocks may be used to perform initial system accessand achieve UL synchronization in a physical random access channel(PRACH) 430. The PRACH 430 carries a random sequence and cannot carryany UL data/signaling. Each random access preamble occupies a bandwidthcorresponding to six consecutive resource blocks. The starting frequencyis specified by the network. That is, the transmission of the randomaccess preamble is restricted to certain time and frequency resources.There is no frequency hopping for the PRACH. The PRACH attempt iscarried in a single subframe (1 ms) or in a sequence of few contiguoussubframes and a UE can make only a single PRACH attempt per frame (10ms).

FIG. 5 is a diagram 500 illustrating an example of a radio protocolarchitecture for the user and control planes in LTE. The radio protocolarchitecture for the UE and the eNB is shown with three layers: Layer 1,Layer 2, and Layer 3. Layer 1 (L1 layer) is the lowest layer andimplements various physical layer signal processing functions. The L1layer will be referred to herein as the physical layer 506. Layer 2 (L2layer) 508 is above the physical layer 506 and is responsible for thelink between the UE and eNB over the physical layer 506.

In the user plane, the L2 layer 508 includes a media access control(MAC) sublayer 510, a radio link control (RLC) sublayer 512, and apacket data convergence protocol (PDCP) 514 sublayer, which areterminated at the eNB on the network side. Although not shown, the UEmay have several upper layers above the L2 layer 508 including a networklayer (e.g., IP layer) that is terminated at the PDN gateway 118 on thenetwork side, and an application layer that is terminated at the otherend of the connection (e.g., far end UE, server, etc.).

The PDCP sublayer 514 provides multiplexing between different radiobearers and logical channels. The PDCP sublayer 514 also provides headercompression for upper layer data packets to reduce radio transmissionoverhead, security by ciphering the data packets, and handover supportfor UEs between eNBs. The RLC sublayer 512 provides segmentation andreassembly of upper layer data packets, retransmission of lost datapackets, and reordering of data packets to compensate for out-of-orderreception due to hybrid automatic repeat request (HARQ). The MACsublayer 510 provides multiplexing between logical and transportchannels. The MAC sublayer 510 is also responsible for allocating thevarious radio resources (e.g., resource blocks) in one cell among theUEs. The MAC sublayer 510 is also responsible for HARQ operations.

In the control plane, the radio protocol architecture for the UE and eNBis substantially the same for the physical layer 506 and the L2 layer508 with the exception that there is no header compression function forthe control plane. The control plane also includes a radio resourcecontrol (RRC) sublayer 516 in Layer 3 (L3 layer). The RRC sublayer 516is responsible for obtaining radio resources (i.e., radio bearers) andfor configuring the lower layers using RRC signaling between the eNB andthe UE.

FIG. 6 is a block diagram of an eNB 610 in communication with a UE 650in an access network. In the DL, upper layer packets from the corenetwork are provided to a controller/processor 675. Thecontroller/processor 675 implements the functionality of the L2 layer.In the DL, the controller/processor 675 provides header compression,ciphering, packet segmentation and reordering, multiplexing betweenlogical and transport channels, and radio resource allocations to the UE650 based on various priority metrics. The controller/processor 675 isalso responsible for HARQ operations, retransmission of lost packets,and signaling to the UE 650.

The TX processor 616 implements various signal processing functions forthe L1 layer (i.e., physical layer). The signal processing functionsincludes coding and interleaving to facilitate forward error correction(FEC) at the UE 650 and mapping to signal constellations based onvarious modulation schemes (e.g., binary phase-shift keying (BPSK),quadrature phase-shift keying (QPSK), M-phase-shift keying (M-PSK),M-quadrature amplitude modulation (M-QAM)). The coded and modulatedsymbols are then split into parallel streams. Each stream is then mappedto an OFDM subcarrier, multiplexed with a reference signal (e.g., pilot)in the time and/or frequency domain, and then combined together using anInverse Fast Fourier Transform (IFFT) to produce a physical channelcarrying a time domain OFDM symbol stream. The OFDM stream is spatiallyprecoded to produce multiple spatial streams. Channel estimates from achannel estimator 674 may be used to determine the coding and modulationscheme, as well as for spatial processing. The channel estimate may bederived from a reference signal and/or channel condition feedbacktransmitted by the UE 650. Each spatial stream is then provided to adifferent antenna 620 via a separate transmitter 618TX. Each transmitter618TX modulates an RF carrier with a respective spatial stream fortransmission.

At the UE 650, each receiver 654RX receives a signal through itsrespective antenna 652. Each receiver 654RX recovers informationmodulated onto an RF carrier and provides the information to thereceiver (RX) processor 656. The RX processor 656 implements varioussignal processing functions of the L1 layer. The RX processor 656performs spatial processing on the information to recover any spatialstreams destined for the UE 650. If multiple spatial streams aredestined for the UE 650, they may be combined by the RX processor 656into a single OFDM symbol stream. The RX processor 656 then converts theOFDM symbol stream from the time-domain to the frequency domain using aFast Fourier Transform (FFT). The frequency domain signal comprises aseparate OFDM symbol stream for each subcarrier of the OFDM signal. Thesymbols on each subcarrier, and the reference signal, is recovered anddemodulated by determining the most likely signal constellation pointstransmitted by the eNB 610. These soft decisions may be based on channelestimates computed by the channel estimator 658. The soft decisions arethen decoded and de-interleaved to recover the data and control signalsthat were originally transmitted by the eNB 610 on the physical channel.The data and control signals are then provided to thecontroller/processor 659.

The controller/processor 659 implements the L2 layer. Thecontroller/processor can be associated with a memory 660 that storesprogram codes and data. The memory 660 may be referred to as acomputer-readable medium. In the UL, the control/processor 659 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the core network. The upper layerpackets are then provided to a data sink 662, which represents all theprotocol layers above the L2 layer. Various control signals may also beprovided to the data sink 662 for L3 processing. Thecontroller/processor 659 is also responsible for error detection usingan acknowledgement (ACK) and/or negative acknowledgement (NACK) protocolto support HARQ operations.

In the UL, a data source 667 is used to provide upper layer packets tothe controller/processor 659. The data source 667 represents allprotocol layers above the L2 layer. Similar to the functionalitydescribed in connection with the DL transmission by the eNB 610, thecontroller/processor 659 implements the L2 layer for the user plane andthe control plane by providing header compression, ciphering, packetsegmentation and reordering, and multiplexing between logical andtransport channels based on radio resource allocations by the eNB 610.The controller/processor 659 is also responsible for HARQ operations,retransmission of lost packets, and signaling to the eNB 610.

Channel estimates derived by a channel estimator 658 from a referencesignal or feedback transmitted by the eNB 610 may be used by the TXprocessor 668 to select the appropriate coding and modulation schemes,and to facilitate spatial processing. The spatial streams generated bythe TX processor 668 are provided to different antenna 652 via separatetransmitters 654TX. Each transmitter 654TX modulates an RF carrier witha respective spatial stream for transmission.

The UL transmission is processed at the eNB 610 in a manner similar tothat described in connection with the receiver function at the UE 650.Each receiver 618RX receives a signal through its respective antenna620. Each receiver 618RX recovers information modulated onto an RFcarrier and provides the information to a RX processor 670. The RXprocessor 670 may implement the L1 layer.

The controller/processor 675 implements the L2 layer. Thecontroller/processor 675 can be associated with a memory 676 that storesprogram codes and data. The memory 676 may be referred to as acomputer-readable medium. In the UL, the control/processor 675 providesdemultiplexing between transport and logical channels, packetreassembly, deciphering, header decompression, control signal processingto recover upper layer packets from the UE 650. Upper layer packets fromthe controller/processor 675 may be provided to the core network. Thecontroller/processor 675 is also responsible for error detection usingan ACK and/or NACK protocol to support HARQ operations.

FIG. 7 is a diagram 700 illustrating a range expanded cellular region ina heterogeneous network. A lower power class eNB such as the RRH 710 bmay have a range expanded cellular region 703 that is expanded from thecellular region 702 through enhanced inter-cell interferencecoordination between the RRH 710 b and the macro eNB 710 a and throughinterference cancellation performed by the UE 720. In enhancedinter-cell interference coordination, the RRH 710 b receives informationfrom the macro eNB 710 a regarding an interference condition of the UE720. The information allows the RRH 710 b to serve the UE 720 in therange expanded cellular region 703 and to accept a handoff of the UE 720from the macro eNB 710 a as the UE 720 enters the range expandedcellular region 703.

FIG. 8 is a diagram illustrating a network 800 which includes a macronode and a number of remote radio heads (RRHs) in accordance withcertain aspects of the present disclosure. The macro node 802 isconnected to RRHs 804, 806, 808, 810 with optical fiber. In certainaspects, network 800 may be a homogeneous network or a heterogeneousnetwork and the RRHs 804-810 may be low power or high power RRHs. In anaspect, the macro node 802 handles all scheduling within the cell, foritself and the RRHs. The RRHs may be configured with the same cellidentifier (ID) as the macro node 802 or with different cell IDs. If theRRHs are configured with the same cell ID, the macro node 802 and theRRHs may operate as essentially one cell controlled by the macro node802. On the other hand, if the RRHs and the macro node 802 areconfigured with different cell IDs, the macro node 802 and the RRHs mayappear to a UE as different cells, though all control and scheduling maystill remain with the macro node 802. It should further be appreciatedthat the processing for the macro node 802 and the RRHs 804, 806, 808,810 may not necessarily have to reside at the macro node. It may also beperformed in a centralized fashion at some other network device orentity that is connected with the macro and the RRHs.

In certain aspects, the term transmission/reception point (“TxP”)typically represents geographically separated transmission/receptionnodes controlled by at least one central entity (e.g., eNodeB), whichmay have the same or different cell IDs.

In certain aspects, when each of the RRHs share the same cell ID withthe macro node 802, control information may be transmitted using CRSfrom the macro node 802 or both the macro node 802 and all of the RRHs.The CRS is typically transmitted from each of the transmission pointsusing the same resource elements, and therefore the signals collide.When each of the transmission points has the same cell ID, CRStransmitted from each of the transmission points may not bedifferentiated. In certain aspects, when the RRHs have different cellIDs, the CRS transmitted from each of the TxPs using the same resourceelements may or may not collide. Even in the case, when the RRHs havedifferent cell IDs and the CRS collide, advanced UEs may differentiateCRS transmitted from each of the TxPs using interference cancellationtechniques and advanced receiver processing.

In certain aspects, when all transmission points are configured with thesame cell ID and CRS is transmitted from all transmission points, properantenna virtualization is needed if there are an unequal number ofphysical antennas at the transmitting macro node and/or RRHs. That is,CRS is to be transmitted with an equal number of CRS antenna ports. Forexample, if the node 802 and the RRHs 804, 806, 808 each have fourphysical antennas and the RRH 810 has two physical antennas, a firstantenna of the RRH 810 may be configured to transmit using two CRS portsand a second antenna of the RRH 810 may be configured to transmit usinga different two CRS ports. Alternatively, for the same deployment, macro802 and RRHs 804, 806, 808, may transmit only two CRS antenna ports fromselected two out of the four transmit antennas per transmission point.Based on these examples, it should be appreciated that the number ofantenna ports may be increased or decreased in relation to the number ofphysical antennas.

As discussed supra, when all transmission points are configured with thesame cell ID, the macro node 802 and the RRHs 804-810 may all transmitCRS. However, if only the macro node 802 transmits CRS, outage may occurclose to an RRH due to automatic gain control (AGC) issues. In such ascenario, CRS based transmission from the macro 802 may be received atlow receive power while other transmissions originating from theclose-by RRH may be received at much larger power. This power imbalancemay lead to the aforementioned AGC issues.

In summary, typically, a difference between same/different cell IDsetups relates to control and legacy issues and other potentialoperations relying on CRS. The scenario with different cell IDs, butcolliding CRS configuration may have similarities with the same cell IDsetup, which by definition has colliding CRS. The scenario withdifferent cell IDs and colliding CRS typically has the advantagecompared to the same cell ID case that system characteristics/componentswhich depend on the cell ID (e.g., scrambling sequences, etc.) may bemore easily differentiated.

The exemplary configurations are applicable to macro/RRH setups withsame or different cell IDs. In the case of different cell IDs, CRS maybe configured to be colliding, which may lead to a similar scenario asthe same cell ID case but has the advantage that system characteristicswhich depend on the cell ID (e.g., scrambling sequences, etc.) may bemore easily differentiated by the UE).

In certain aspects, an exemplary macro/RRH entity may provide forseparation of control/data transmissions within the transmission pointsof this macro/RRH setup. When the cell ID is the same for eachtransmission point, the PDCCH may be transmitted with CRS from the macronode 802 or both the macro node 802 and the RRHs 804-810, while thePDSCH may be transmitted with CSI-RS and DM-RS from a subset of thetransmission points. When the cell ID is different for some of thetransmission points, PDCCH may be transmitted with CRS in each cell IDgroup. The CRS transmitted from each cell ID group may or may notcollide. UEs may not differentiate CRS transmitted from multipletransmission points with the same cell ID, but may differentiate CRStransmitted from multiple transmission points with different cell IDs(e.g., using interference cancellation or similar techniques).

In certain aspects, in the case where all transmission points areconfigured with the same cell ID, the separation of control/datatransmissions enables a UE transparent way of associating UEs with atleast one transmission point for data transmission while transmittingcontrol based on CRS transmissions from all the transmission points.This enables cell splitting for data transmission across differenttransmission points while leaving the control channel common. The term“association” above means the configuration of antenna ports for aspecific UE for data transmission. This is different from theassociation that would be performed in the context of handover. Controlmay be transmitted based on CRS as discussed supra. Separating controland data may allow for a faster reconfiguration of the antenna portsthat are used for a UE's data transmission compared to having to gothrough a handover process. In certain aspects, cross transmission pointfeedback may be possible by configuring a UE's antenna ports tocorrespond to the physical antennas of different transmission points.

In certain aspects, UE-specific reference signals enable this operation(e.g., in the context of LTE-A, Rel-10 and above). CSI-RS and DM-RS arethe reference signals used in the LTE-A context. Interference estimationmay be carried out based on or facilitated by CSI-RS muting. Whencontrol channels are common to all transmission points in the case of asame cell ID setup, there may be control capacity issues because PDCCHcapacity may be limited. Control capacity may be enlarged by using FDMcontrol channels. Relay PDCCH (R-PDCCH) or extensions thereof, such asan enhanced PDCCH (ePDCCH) may be used to supplement, augment, orreplace the PDCCH control channel.

CSI-RS Group Definition

In general, the macro node 802 and RRHs may be assigned a subset of theCSI-RS ports. For example, if there are 8 available CSI-RS ports, themacro 802 may be assigned to transmit on CSI-RS ports 0, 1, RRH 804 maybe assigned to transmit on CSI-RS ports 2, 3, RRH 806 may be assigned totransmit on CSI-RS ports 4, 5, RRH 808 may be assigned to transmit onCSI-RS ports 6, 7, and RRH 810 may not be assigned any CSI-RS ports.

Alternatively, the macro node 802 and/or the RRHs may be assigned thesame CSI-RS ports. For example, the macro 802, RRH 804 and RRH 808 maybe assigned to transmit on CSI-RS ports 0, 1, 2, 3, and RRH 806 and RRH810 may be assigned to transmit on CSI-RS ports 4, 5, 6, and 7. In sucha configuration, the CSI-RS from the macro 802 as well as RRHs 804, 808would overlap and the CSI-RS from RRHs 806, 810 would overlap.

In LTE Rel-10, CSI-RS was introduced to facilitate channel feedbackreporting and either 1, 2, 4, or 8 CSI-RS ports may be configured fornon-zero power transmission. The concepts discussed supra may utilizethe Rel-10 CSI-RS but further enhancements are possible in futurereleases or in related transmission systems. For example, in one aspect,the number of configurable CSI-RS ports may be increased which wouldenable more flexibility in configuring CSI-RS ports.

In one aspect, the concept of CSI-RS groups is considered. A CSI-RSgroup may be defined as a set of CSI-RS ports that is grouped togetherfor the purpose of facilitating CSI-RS configuration, CSI feedbackreporting, or any other aspects that build on the CSI-RS. Similar to theprevious examples, consider the case in which there is a total of 10CSI-RS ports. Macro 802 may be configured with CSI-RS ports 0, 1, RRH804 may be assigned CSI-RS ports 2, 3, RRH 806 may be assigned CSI-RSports 4, 5, RRH 808 may be assigned CSI-RS ports 6, 7 and RRH 810 may beassigned CSI-RS ports 8, 9. The CSI-RS ports assigned to eachtransmission point may be grouped, that is, CSI-RS ports 0, 1 would formCSI-RS group 0, CSI-RS ports 2, 3 would form group 1, etc. In this way,each transmission point may be associated with a CSI-RS group which maybe an embodiment of practical importance. However, as noted supra,CSI-RS groups need not be restricted to the antennas of a singletransmission point; instead, they may span multiple transmission points.

In one aspect, CSI-RS ports may be enumerated consecutively, as done inthe above examples. However, such numbering definition is not essentialto the procedures described herein. Alternatively, the grouping may bedescribed by configuring CSI-RS groups and enumerating CSI-RS portswithin each group starting with zero. Further, CSI-RS groups may also bereferred to as CSI-RS resources or CSI-RS patterns.

In another aspect, CSI-RS groups may be transmitted with differentparameters, e.g., periodicity, power-level, or similar aspects. Suchparameters may be common among the CSI-RS ports of a specific CSI-RSgroup or may be communicated to the UE for each CSI-RS group.

The CSI-RS configuration may be UE-specific. Each UE may be configuredwith up to a predetermined number of CSI-RS ports (e.g., 8 CSI-RS ports)and/or a predetermined number of CSI-RS groups. The UE may furtherreceive CSI-RS transmissions from different transmission points,including but not limited to the macro and RRH nodes. For example, theUE 820 may receive CSI-RS on CSI-RS ports 0, 1 from macro 802, CSI-RS onCSI-RS ports 2, 3 from RRH 804, CSI-RS on CSI-RS ports 4, 5 from RRH806, and CSI-RS on CSI-RS ports 6, 7 from RRH 808. Such a configurationis typically specific to the UE 820. For example, the UE 822 may also beconfigured with 8 CSI-RS ports and receive CSI-RS on CSI-RS ports 0, 1from RRH 808, CSI-RS on CSI-RS ports 2, 3 from RRH 810, CSI-RS on CSI-RSports 4, 5 from RRH 804, and CSI-RS on CSI-RS ports 6, 7 from RRH 806.Generally, for any particular UE, the CSI-RS ports may be distributedamong the RRHs and the particular UE may be configured with any numberof the CSI-RS ports to receive CSI-RS on those ports from RRHsconfigured to send on those ports to the particular UE. It should beappreciated that the concept described above goes beyond the specificnumbering scheme that was used in this example. The concept of CSI-RSgroups spans both numbering definitions.

As discussed supra, UEs may receive CSI-RS transmissions and may provideCSI feedback based at least in part on these CSI-RS. An issue is thatthe codebooks of LTE Release 10 and prior releases were designedassuming that the path loss for each of the CSI-RS ports is equal andmay therefore suffer some performance loss if this condition is notsatisfied. Because multiple RRHs may be transmitting data with CSI-RS,the path loss associated with each of the CSI-RS may be different. Assuch, codebook refinements may be needed to enable cross transmissionpoint CSI feedback that takes into account the proper path losses toTxPs. Multiple CSI feedback may be provided by grouping antenna portsand providing feedback per group.

The UE may provide CSI feedback based on its CSI-RS configuration whichmay include PMI/RI/CQI. The codebook design may assume that the antennasare not geographically separated, and therefore that there is the samepath loss from the antenna array to the UE. This is not the case formultiple RRHs, as the antennas are uncorrelated and see differentchannels. Codebook refinements may enable more efficient cross TxP CSIfeedback. CSI estimation may capture the path loss difference betweenthe antenna ports associated with different TxPs.

CSI-RS Based Selection and Reporting of Transmission Points

In macro/RRH setups, CSI-RS and DM-RS may be used to decouple controland data transmission. Data transmission (e.g. for LTE Rel 10 andbeyond) may be based on CSI-RS and DM-RS, while control may be receivedfrom a possibly different set of transmission points via CRS.Traditionally, selection of transmission points for data transmission isbased on monitoring CRS. In such a setup CSI-RS configuration may followUE reporting of RSRP, RSRQ or other metrics based on CRS. However, dueto decoupling of control and data transmission, the CRS may not beavailable for selecting transmission points for data transmission.Therefore, a need exists for an alternative to CRS based configurationof data-serving transmission points.

Certain aspects of the present disclosure introduce a reportingframework (e.g., in LTE Rel-11), in which this can be carried out basedon CSI-RS. In certain aspects, the new concept of CSI-RS groups, i.e., aset of CSI-RS ports of a UE that a UE considers as one group forPMI/CQI/RI reporting, may be defined. Specifically, a UE may consider agroup by itself and perform reporting (e.g., similar to Rel-10 CSIreporting in TM9), except that it may disregard all CSI-RS outside aspecific CSI-RS group. Details of how the reporting/signaling andconfiguration of CSI-RS groups may be performed are discussed herein.The concepts described herein may be applicable to both macro/RRH setupswith same or different cell ID.

Configuration of CSI-RS Groups

FIG. 9 is a diagram illustrating CSI-RS groups corresponding todifferent transmission points in accordance with certain aspects of thepresent disclosure. Network 900 includes macro eNB 902 with a coveragearea 920, and RRHs 904, 906, 908 and 910 with respective coverage areas912, 914, 916 and 918. In certain aspects each CSI-RS group maycorrespond to the antennas of a different macro/RRH transmission points.For example, as shown in FIG. 9, CSI-RS group 0 corresponds to macro eNB902, CSI-RS group 1 corresponds to RRH 908, CSI-RS group 2 correspondsto RRH 906, CSI-RS group 3 corresponds to RRH 910 and CSI-RS group 4corresponds to RRH 904.

FIG. 10 is a diagram illustrating CSI-RS groups in which multiplecells/TxPs form each CSI-RS group in accordance with certain aspects ofthe present disclosure. In network 1000, CSI-RS groups are configured toinclude antennas from multiple cells. For example, as shown, CSI-RSgroup 0 corresponds to macro eNB 902, CSI-RS group 1 corresponds toantennas of RRHs 908 and 910. Similarly, CSI-RS group 2 corresponds toantennas of RRHs 904 and 906.

According to certain aspects, not shown herein, the CSI-RS groupconfigurations may include partial assignments of antennas fromdifferent transmission points. CSI-RS groups may also be configured inan overlapping fashion. For example, in the FIG. 10, the RRH 910 may bepart of both the group 1 and group 2 CSI-RS groups (not shown in thefigure). In certain aspects, CSI-RS group configuration may be madeknown to the UE, e.g., together with the CSI-RS port/patternconfiguration. According to certain aspects, being able to assign samescrambling IDs across different cells may be beneficial for thedifferent cell ID cases. According to other aspects, differentscrambling IDs may be assigned to each CSI-RS group, even if the CSI-RSgroups have the same cell ID.

In certain aspects, overlapping CSI-RS groups may be configured fordifferent RRHs, e.g., according to the intended CoMP transmissionconfiguration to allow more accurate SINR measurements. Beamforming onsome CSI-RS ports may be part of this configuration to facilitate moreaccurate rate prediction (e.g., CQI feedback). A UE may measure channelfrom its CSI-RS ports and the transmission from other overlapping CSI-RStransmissions would be interference. This enables UEs to measure channelstate conditions and interference on a resource specific basis. In suchcase, the CSI-RS may be regarded as a resource quality indicationreference signal (RQI-RS). Alternately, in another design, the UE mayreport based on several different sets of CSI-RS groups and the eNB mayperform rate prediction based on these reports by extrapolation.

In certain aspects, CSI-RS reporting by the UE may not take into accountdifferent transmit power levels of macro and RRH. The eNB may have totake this into account, especially when performing joint transmission,i.e., the final CQI may need to be adjusted accordingly in case a jointtransmission takes place from both macro and RRH. In an aspect, CSI-RSgrouping may be according to the power class of nodes (e.g., macro andRRH nodes, pico nodes, femto, etc.). Grouping according to the powerclass of nodes may facilitate taking into account the different powerlevels of macro and RRH, respectively, for reporting and scheduling.

Extending CSI Reporting Modes to Reflect CSI-RS Groups

In certain aspects, CSI-RS groups may be viewed as an additional“dimension” of a UE's CSI reporting. In a first aspect, reporting maydecouple CSI-RS group specific reporting from the CSI reporting's otherdimensions (e.g., frequency-domain subband cycling, etc.). In a secondaspect, reporting may be done jointly across these different dimensions.Both these aspects are further described herein.

Referring to the first aspect, described above, CSI-RS group specificreporting may not be “mixed” with existing dimensions. UEs may reportPMI/CQI/RI for different CSI-RS groups separately (i.e., the wayPMI/CQI/RI is reported within a CSI-RS group is not changed). Tworeporting strategies are described herein with respect to the firstaspect. First, eNBs may configure predefined cycling through CSI-RSgroups. Second, UEs may report the best-N_(G) CSI-RS groups. Either ofthe above two reporting strategies may be incorporated into the existingCSI reporting modes, both aperiodic and periodic.

For periodic reporting, the cycling may be incorporated, for example,into the existing PUCCH 2-1 reporting modes, which currently has cyclingacross bandwidth parts. The selection and reporting of the best-N_(G)CSI-RS groups may follow a reporting approach similar to current PUCCH2-1 or PUSCH 2-2. For aperiodic reporting, payload could be increased toaccommodate the CSI report from multiple CSI-RS groups. This may be anoption especially for those modes that carry relatively little payloadtoday.

Referring to the second alternative, joint reporting across differentdimensions, certain aspects consider CSI-RS groups as another dimensionfor augmenting CSI-RS modes. In an aspect, a UE may report the best-Msubbands from a selected set of CSI-RS groups. For instance, a UE mayreport sub-band SB1 for the first CSI-RS group and SB2 for a secondCSI-RS group, depending on channel condition. This may be incorporatedinto the existing reporting modes by adding an indicator that the UEcould use to indicate the reported CSI-RS group. For example, thisindicator may be an index or bitmap linking the radio resource control(RRC) configuration of the CSI-RS group to the CSI-RS configuration.

In certain aspects, it is also possible to have some predefined cyclingpattern for reporting the CSI-RS groups. FIGS. 11-12 illustrate examplesof different cycling patterns. The figures show CSI-RS Groups 1, 2 and 3with each CSI-RS group including four bandwidth parts BWP1, BWP2, BWP3and BWP4. The shaded squares 1102, 1202 denote reporting instances.

The example predefined cycling pattern of FIG. 11 cycles across a subsetof the CSI-RS groups first, and then in a second step cycles across thebandwidth. For instance, a UE reports BWP1 of CSI-RS Group 1 followed byBWP1 of CSI-RS Group 2, etc. until all groups are reported, and then inanother cycle reports BWP2 of all the Groups, and so on.

The example predefined cycling pattern of FIG. 12 cycles across BWPs ofthe CSI-RS Group 1 first, and then cycles across the BWPs of otherCSI-RS Groups 2, 3 and 4.

Many other combinations may be possible. In an aspect, a frequencygranularity other than a bandwidth part may be chosen (e.g., a subbandor some other granularity). As well, UE selection based reporting may beincorporated into the above framework.

In certain aspects, signaling of codebooks to use per CSI-RS group (orfor different CSI-RS group combinations as described later on) may bebeneficial, especially if codebook enhancements are defined as part ofLTE Rel-11 or beyond. In an aspect, the concepts described herein mayrely on the existing 2Tx, 4Tx, 8Tx codebooks. Enhanced codebooks orinter-cell feedback may be introduced in later releases (e.g., Rel-11and later). Such codebooks may readily leverage the CSI-RS groupconcepts described herein. The reporting based on different CSI-RSgroups may be linked to different codebook sets, either implicitly orexplicitly. Codebook sets may encompass existing Rel-10 codebooks aswell as new codebooks potentially defined in later releases.

The CSI-RS group based reporting has the benefit that interferenceestimation may implicitly be made part of the PMI/CQI/RI report (i.e.,assumptions on interference estimation may be made consistent withassumptions on the CSI-RS group configuration). According to certainaspects, CRS based reporting may be potentially considered as a“virtual” CSI-RS group and a UE may provide feedback consistent withthis assumption to provide additional information to the eNodeB.

Certain aspects may exploit subframe specific CSI-RS group configurationbased on subframe-specific reporting concept of Rel-10 eICIC. Thisconcept may be exploited to have different CSI-RS group configurationsin different subframes. For example, CSI grouping 1 for subframe set 1;another possible CSI grouping 2 for subframe set 2; and possibly anotherdefinition for the complementary set (as currently defined as part ofRel-10). This may also leverage existing reporting concepts, althoughextensions may be considered. This may be used for heterogeneousnetworks, similar to the way CQI is reported for conventional HetNet.Further, this may be advantageous if a UE is served (transparently) bydifferent transmission points in different subframes).

According to certain aspects, an eNodeB may restrict reporting to asubset of CSI-RS groups, similar to codebook subset restriction,throughout all the above concepts.

Certain aspects may limit reporting payload if multiple CSI-RS groupsare reported together. The set S (as defined in LTE specifications) maybe the same for all CSI-RS groups but the configuration of the set S maybe such that it cycles over subband or bandwidth parts (and over timetherefore cycles across the entire bandwidth). The set S may bedifferent across CSI-RS groups and, for example, may be mutuallyorthogonal to each other or overlapped. It may cover the entirebandwidth across all groups.

Certain aspects may relate to differential feedback encoding. Forexample, CQI (and CSI information in general) may be encodeddifferentially. This is especially useful if CSI-RS groups overlap,leading to correlation among CSI reports for different group. Thiscorrelation may be exploited to reduce uplink feedback overhead, e.g.,in a similar manner as the differential CQI encoding employed in Rel-10.

The above description considered the introduction of CSI-RS groups intothe existing CSI reporting framework (e.g. Rel-10 CSI reportingframework). In certain aspects, CSI-RS groups may be used to supportexplicit feedback reporting. For example, explicit feedback of thedominant eigen-direction and/or eigen-values associated with MIMOstreams of different CSI-RS groups may be considered. In an aspect, UEsmay consider combining different CSI-RS groups and provide feedbackbased on the combined CSI-RS ports of the aggregated groups. Forexample, if groups consist of 2 CSI-RS ports each, then a UE may providefeedback of 2 aggregated groups (thus 4 CSI-RS ports total), or 4aggregated CSI-RS groups (8 CSI-RS ports total). Feedback computationmay be based on available codebooks for the resulting number of CSI-RSports.

The aggregation of groups may have different performance. The UE maypick a good configuration and provide an indication of which aggregationshould be used. Conceptually, this may be similar to the rank-indicator;and may be referred to as “CSI-RS group selection indicator.”

When aggregating multiple CSI-RS groups, a UE may need to makeassumptions on the relative phases between these CSI-RS groups as thismay impact the performance of the aggregated CSI-RS configuration.Various assumptions may be made by the UE. In one aspect, the UE mayassume that the phase relationship between the CSI-RS groups consideredfor aggregation is determined by the phase relationship observed betweenthe CSI-RS groups. In another aspect, a specific phase relationship maybe assumed by the UE. This relationship may be signaled to the UE aspart of the CSI-RS configuration or feedback reporting configuration. Inyet another aspect, the UE may perform averaging across different phaserelationships between the CSI-RS groups. Additional signaling maysupport this operation by providing details on how the averaging is tobe performed.

Signaling and Triggering CSI-RS Group Reports

In certain aspects, as part of configuring CSI-RS groups, CSI-RSgrouping may be made part of the CSI-RS and muting configuration and besignaled semi-statically.

In certain aspects, as part of triggering CSI reports belonging tocertain CSI-RS groups, an eNB may dynamically signal a referencesindicating which CSI-RS group to use for reporting (that reference coulde.g. point to the RRC-based CSI-RS configuration). A bitmask may be usedto select multiple CSI-RS groups for reporting at the same time. In anaspect, aperiodic triggering may be similar to the way aperiodic SRS istriggered in Rel-10. For periodic reporting, eNodeB may configure thereporting techniques discussed previously through signaling to the UE.

In certain aspects, CSI-RS group indication made by the UE may besimilar to rank indicator as previously discussed and may be used to cutback on signaling overhead. For example, an eNB may exploit 1-bitsignaling, indicating whether or not it is following the UE's CSI-RSgroup indication. If the eNB decides not to follow the UE's suggestion,the bitmask-based signaling mentioned above (or a variation thereof) maybe needed.

FIG. 13 illustrates example operations 1300 performed, for example, by atransmitter, in a system comprising a macro node and at least one remoteradio head (RRH) entity, in accordance with certain aspects of thepresent disclosure. Operations 1300 may be executed, for example atprocessor(s) 616 and/or 675 of the eNB 610.

Operations 1300 may begin at 1302 by determining one or more CSI-RSgroups for feedback reporting by a UE (e.g. UE 820). For example, asdiscussed with reference to FIGS. 9 and 10, each CSI-RS group maycorrespond to antennas of a different TxP or may be configured toinclude antennas from multiple TxPs.

At 1304, an indicator identifying the one or more CSI-RS groups may betransmitted to the UE. The UE may use the received indicator todetermine the CSI-RS groups and provide feedback to an eNB (e.g. macronode 802) for one or more CSI-RS groups.

At 1306, feedback reports may be received at an eNB from the UEcorresponding to one or more of the CSI-RS groups. As discussed above, aUE may either report the best-N_(G) CSI-RS groups or cycle across theCSI-RS groups one by one, or perform reporting of the CSI-RS groups inaccordance with the above description.

The operations 1300 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 13. For example, operations 1300 illustrated in FIG.13 correspond to components 1300A illustrated in FIG. 1300A. In FIG.1300A, a CSI-RS groups determiner 1302A may determine one or more CSI-RSgroups. A transmitter 1304A may transmit an indicator identifying theCSI-RS groups, and a receiver 1306A may receive feedback reports from aUE 650 corresponding to the one or more CSI-RS groups. The receivedfeedback reports may be processed in a processor 670 at eNB 610.

FIG. 14 illustrates example operations 1400 performed, for example, by aUE, in a system comprising a macro node and at least one remote radiohead (RRH) entity, in accordance with certain aspects of the presentdisclosure. Operations 1400 may be executed, for example at processor(s)656 and/or 658 of UE 650.

Operations 1400 may begin at 1402 by determining one or more CSI-RSgroups that a UE groups for feedback reporting. For example, asdiscussed with reference to FIGS. 9 and 10, each CSI-RS group maycorrespond to antennas of a different TxP or may be configured toinclude antennas from multiple TxPs.

At 1404, the UE may perform channel measurements for the CSI-RS groups.For example, the UE may measure a channel from the CSI-RS ports of oneor more CSI-RS groups.

At 1406, feedback reports corresponding to channel measurements of atleast one of the CSI-RS groups may be transmitted to a macro node (e.g.macro node 802). As discussed above, a UE may either report thebest-N_(G) CSI-RS groups or cycle across the CSI-RS groups one by one orperform reporting of the CSI-RS groups in accordance with the abovedescription.

The operations 1400 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 14. For example, operations 1400 illustrated in FIG.14 correspond to components 1400A illustrated in FIG. 1400A. In FIG.1400A, a CSI-RS groups determiner 1402A may determine one or more CSI-RSgroups. A channel measurer 1404A may measure channel for the CSI-RSgroups. Finally, a transceiver (TX/RX) 1406A may transmit feedbackreports to an eNB 610 for the CSI-RS groups.

FIG. 15 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1500 employing a processing system 1510.The processing system 1510 may be implemented with a bus architecture,represented generally by the bus 1530. The bus 1530 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1510 and the overall designconstraints. The bus 1530 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1524, the modules 1520, 1522, and the computer-readable medium 1526. Thebus 1530 may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, whichare well known in the art, and therefore, will not be described anyfurther.

The processing system 1510 is coupled to a transceiver 1540. Thetransceiver 1540 is coupled to one or more antennas 1550. Thetransceiver 1540 provides a means for communicating with various otherapparatus over a transmission medium. The processing system 1510includes a processor 1524 coupled to a computer-readable medium 1526.The processor 1524 is responsible for general processing, including theexecution of software stored on the computer-readable medium 1526. Thesoftware, when executed by the processor 1524, causes the processingsystem 1510 to perform the various functions described supra for anyparticular apparatus. The computer-readable medium 1526 may also be usedfor storing data that is manipulated by the processor 1524 whenexecuting software. The processing system further includes modules 1520and 1522. The modules may be software modules running in the processor1524, resident/stored in the computer readable medium 1526, one or morehardware modules coupled to the processor 1524, or some combinationthereof. The processing system 1510 may be a component of the UE 650 andmay include the memory 660 and/or at least one of the TX processor 668,the RX processor 656, and the controller/processor 659.

Enhancing Codebook Design for Geographically Separated Antennas

With the MIMO codebooks defined in LTE, only co-located antennas may beaddressed efficiently, since the codebooks assume that all transmitantennas' signals are received with the same (long term) average power.In addition to the aspects and methods discussed supra, one may considerenhanced codebooks which may include codebook entries addressingmultiple separate groups of antennas. This is a straightforwardextension of Rel-8/9/10 closed loop feedback. However, it may likelyrequire new codebook design for adequate performance. For example,precoder subsets with “antenna turn off” may enable fast cell selection.

In yet another aspect, related to the concepts discussed earlier, the UEmay report independent RI and PMI for two or more configured CSI-RSgroups. In addition, the UE may also report an explicit index indicatingwhich antenna group is addressed by additional subband CQI information.For example, separate CSI-RS group specific wideband RI/PMI/CQI may beused while subband CQI may be only for an indicated CSI-RS group. Thisapproach may be viewed as an extension of best-m reporting with explicitbest CSI-RS group selection and may be best suited for dynamic pointselection.

In certain aspects, the number of potential feedback candidatetransmission point antennas may exceed the number of antennas definedfor the current codebooks. In order to address this, the UE may reportthe set of detected candidate transmission points, from which the eNBmay select an appropriate reporting set using one of the methodsdescribed above.

Implicitly Linking Aperiodic (A-CSI) Reports to CSI-RS Resources

In certain versions of a standard (e.g., LTE REL-10), there may belittle or no ambiguity with respect to CSI-RS reporting as there is atmost one CSI-RS configuration with non-zero power. Therefore, asconfigured or requested by the network, a UE may employ at most oneCSI-RS configuration for CSI measurement and report back the CSI that isaligned with the configured resource. There is generally no need tosignal to the UE which CSI-RS configuration to use as there is at mostone such configuration for channel quality measurement.

However, as discussed above it may be possible to configure multiplenon-zero power CSI-RS resources (or groups) in later versions of thestandard (e.g., LTE REL-11). As such, it may be necessary to inform theUE which of these multiple CSI-RS resources to report. In an aspect, theUE may be told the specific CSI-RS resource(s) it should report byincluding explicit signaling in the grant requesting such report.However, this may include additional signaling impact as additionalresources (e.g. bits) may need to be allocated in the UE grant for suchexplicit signaling. Techniques for CSI-RS resource selection by the UEwith reduced signaling impact are therefore desirable.

In certain aspects, instead of explicitly signaling to the UE whichCSI-RS resources it may select for CSI feedback reporting, the UE may beimplicitly triggered based on some information the UE already has, e.g.which subframe a reporting request was received. This may save theadditional bits for signaling the CSI-RS resources in the UE grant, thusavoiding or reducing the signaling impact.

In certain aspects, for periodic feedback reporting, each CSI-RSresource may have its reporting instance. Thus, no issues may exist.However, for aperiodic CSI (A-CSI) reporting, the UE may have todetermine the CSI-RS resources for which it should report CSI either byreceiving explicit signaling or implicitly.

In certain aspects, for aperiodic CSI feedback reporting, a dynamictrigger is sent to the UE through a grant that requests an aperiodic CSItransmission by the UE. The CSI-RS resources may be assigned todifferent subframes. In an aspect, the grant defines a referencesubframe for the CSI-RS resource(s). The UE may report CSI for one ormore CSI-RS resources based on the reference subframe which may bedetermined in line with the procedures described in 3GPP specifications.

For a first aspect, if the UE is reporting for a single CSI-RS resource,the UE may report CSI for the CSI-RS resource that either is carried bythe CSI reference subframe or, if the CSI reference subframe does notcarry CSI-RS, an earliest CSI-RS carrying subframe preceding the CSIreference subframe. In an aspect, the eNB and the UE typically know thesubframes on which CSI-RS is transmitted.

For a second aspect, if the UE is reporting for multiple CSI-RSresources, the UE may be signaled a set of CSI-RS resources for which itshould report CSI. In an aspect, the set of CSI-RS resources may beconfigured via RRC signaling. For example, the UE may report the Klatest CSI-RS resources. The parameter K may be configured via RRCsignaling. K may also be defined in line with the first aspect discussedabove.

For a third aspect, the UE may report based on subframe sets. MultipleA-CSI subframe sets may be configured through RRC signaling forincreased flexibility, such that different subframe sets map todifferent CSI-RS resources. In this aspect, if an A-CSI request is sentin certain subframes of a subframe set, the UE reports on CSI-RSresource mapped to the subframe set.

For example two A-CSI subframe sets, A-CSI 1 and A-CSI2, may beconfigured through RRC signaling. Subframe set A-CSI 1 may includesubframes 1, 2, 3, 6, 7 and 8, and may map to CSI-RS resource 1.Similarly subframe set A-CSI 2 may include subframes 0, 4, 5 and 9, andmay map to CSI-RS resource 2. For an example CSI reporting according tothe third aspect, if an A-CSI request is sent on any one of thesubframes 1, 2, 3, 6, 7 or 8 the UE may report for CSI-RS resource 1 andif an A-CSI request is sent on any one of the subframes 0, 4, 5 or 9,the UE may report for CSI-RS resource 2. In an aspect one or moresubframes of a subframe set may be mapped to multiple CSI-RS resources.For example, if subframe set A-CSI 2 included subframes 0, 3, 4, 5, 9,an A-CSI request on subframe 3 may trigger reporting of both CSI-RS 1and CSI-RS 2.

In certain aspects, multiple CSI-RS resources may be present in a samesubframe. In order to avoid inter resource interference, the CSI-RSresources in the same subframe may maintain orthogonality by usingdifferent CSI-RS patterns. In addition, different periodicities may beconfigured for the CSI-RS resources within a same subframe. This way,multiple CSI-RS resources may coincide in the same subframe only incertain subframes.

For example, FIG. 16 illustrates an example configuration 1600 of threeCSI-RS resources in a single subframe in accordance with certain aspectsof the present disclosure. As shown in FIG. 16, CSI-RS resource 1 isconfigured with a 5 ms periodicity, CSI-RS resource 2 is configured witha 10 ms periodicity and CSI-RS 3 is configured with a periodicity of 20ms. Thus, a subframe may have all three CSI-RS resources only every 20ms.

In certain aspects, implicit triggering may be used for the case whensubframes may have multiple CSI-RS resources. For a first aspect, ifmultiple CSI-RS resources are present in the reference subframe, thenthe UE may send a CSI report encompassing all of them. In this aspect,payload considerations may not be a significant concern for A-CSIreporting, since the aperiodic reports are generally carried on the ULdata channel.

For a second aspect, only the first M CSI-RS resources of the referencesubframe may be reported, where M may be configured via RRC signaling.In an aspect M may be influenced by a maximum supportable payload or byconstraints on UE processing.

For a third aspect, if the CSI-RS resources are configured to belong todifferent subframe sets, the UE may report for a first CSI-RS resourceof the different subframe sets.

For a fourth aspect, a bitmap may be signaled to the UE via RRCsignaling that specifies which CSI-RS resources and/or how many CSI-RSresources (e.g. via parameter M above) is to be reported depending onthe reference subframe.

FIG. 17 is a diagram illustrating example operations 1700 performed, forexample, by a user equipment (UE), for implicitly triggering CSIreporting in accordance with certain aspects of the present disclosure.Operations 1700 may be executed, for example at processor(s) 656 and/or658 of UE 650.

At 1702, operation 1700 may begin, by receiving a request for an A-CSIfeedback report (e.g. from an eNB 610). As discussed above, foraperiodic CSI feedback reporting, a dynamic trigger may be received atthe UE through a grant that requests an aperiodic CSI transmission bythe UE.

At 1704, a set of one or more reference CSI-RS resources may bedetermined for feedback reporting, at least in part based on a time inwhich the request was received. As discussed above, for aperiodic CSIreporting, the CSI reference resource may be determined based on thesubframe in which the request for the aperiodic report was received.This determination may also depend on other parameters such as the typeof grant triggering the aperiodic CSI request. As discussed withreference to FIGS. 9 and 10, each CSI-RS resource may correspond toantennas of a different TxP or may be configured to include antennasfrom multiple TxPs.

At 1706, the feedback report is generated based on the set of one ormore reference CSI-RS resources. As discussed above, the UE may measurea channel from the CSI-RS ports of the CSI-RS resources and generatefeedback reports corresponding to the channel measurements.

Finally, at 1708, the generated feedback report may be transmitted toe.g. eNB 610. As discussed above, the UE may either report thebest-N_(G) CSI-RS resources, cycle across the CSI-RS resources one byone, or perform reporting of the CSI-RS resources in accordance with theabove description.

The operations 1700 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 17. For example, operations 1700 illustrated in FIG.17 correspond to components 1700A illustrated in FIG. 1700A. In FIG.1700A, a receiver 1702A may receive a request for an A-CSI feedbackreport. A reference CSI-RS resource determiner 1704A may determine a setof one or more reference CSI-RS resources for feedback reporting. Afeedback report generator 1706A may generate the feedback report.Finally, a transmitter 1708A may transmit the generated feedback reportto an eNB 610.

FIG. 18 is a diagram illustrating an example of a hardwareimplementation for an apparatus 1800 employing a processing system 1810in accordance with certain aspects of the present disclosure. Theprocessing system 1810 may be implemented with a bus architecture,represented generally by the bus 1830. The bus 1830 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 1810 and the overall designconstraints. The bus 1830 links together various circuits including oneor more processors and/or hardware modules, represented by the processor1824, the modules 1820, 1822, and the computer-readable medium 1826. Thebus 1830 may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, whichare well known in the art, and therefore, will not be described anyfurther.

The processing system 1810 is coupled to a transceiver 1840. Thetransceiver 1840 is coupled to one or more antennas 1850. Thetransceiver 1840 provides a means for communicating with various otherapparatus over a transmission medium. The processing system 1810includes a processor 1824 coupled to a computer-readable medium 1826.The processor 1824 is responsible for general processing, including theexecution of software stored on the computer-readable medium 1826. Thesoftware, when executed by the processor 1824, causes the processingsystem 1810 to perform the various functions described supra for anyparticular apparatus. The computer-readable medium 1826 may also be usedfor storing data that is manipulated by the processor 1824 whenexecuting software. The processing system further includes modules 1820and 1822. The modules may be software modules running in the processor1824, resident/stored in the computer readable medium 1826, one or morehardware modules coupled to the processor 1824, or some combinationthereof. The processing system 1810 may be a component of the UE 650 andmay include the memory 660 and/or at least one of the TX processor 668,the RX processor 656, and the controller/processor 659.

FIG. 19 illustrates example operations 1900 performed, for example, by abase station, in accordance with certain aspects of the presentdisclosure. Operations 1900 may be executed, for example at processor(s)616 and/or 675 of the eNB 610.

At 1902, operations 1900 may begin by determining a map correlatingCSI-RS resources with a CSI feedback report request based, at least inpart, on a timing of the request. As discussed above, for aperiodic CSIreporting, the CSI reference resource may be determined based on thesubframe in which the request for the aperiodic report is sent. The eNBgenerally stores a map correlating the CSI-RS resources with thesubframe in which the CSI feedback report request is sent.

At 1904, a set of one or more reference CSI-RS resources may bedetermined for feedback reporting. As discussed with reference to FIGS.9 and 10, each CSI-RS resource may correspond to antennas of a differentTxP or may be configured to include antennas from multiple TxPs.

At 1906, a request may be transmitted for a CSI feedback report at atime, based at least in part on a mapping of the set of one or morereference CSI-RS resources to the time. For example, the eNB maytransmit the request in a subframe mapped to the set of CSI-RS resourcesdetermined at step 1904.

Finally, at 1908, a feedback report may be received based on the set ofone or more reference CSI-RS resources. As discussed above, the UE maymeasure a channel from the CSI-RS ports of the CSI-RS resources andgenerate feedback reports corresponding to the channel measurements.

The operations 1900 described above may be performed by any suitablecomponents or other means capable of performing the correspondingfunctions of FIG. 19. For example, operations 1900 illustrated in FIG.19 correspond to components 1900A illustrated in FIG. 19A. In FIG. 19A,a map determiner 1902A may determine a map correlating CSI-RS resourceswith a CSI feedback report request. A CSI-RS resources determiner 1904Amay determine a set of one or more reference CSI-RS resources forfeedback reporting. A transmitter 1906A may transmit a request for a CSIfeedback report, to for e.g. a UE 650, and a receiver 1908A may receivefeedback reports from the UE 650 based on the set of one or morereference CSI-RS resources. The received feedback reports may beprocessed in a processor 670 at eNB 610.

FIG. 20 is a diagram illustrating an example of a hardwareimplementation for an apparatus 2000 employing a processing system 2010in accordance with certain aspects of the present disclosure. Theprocessing system 2010 may be implemented with a bus architecture,represented generally by the bus 2030. The bus 2030 may include anynumber of interconnecting buses and bridges depending on the specificapplication of the processing system 2010 and the overall designconstraints. The bus 2030 links together various circuits including oneor more processors and/or hardware modules, represented by the processor2024, the modules 2020, 2022, and the computer-readable medium 2026. Thebus 2030 may also link various other circuits such as timing sources,peripherals, voltage regulators, and power management circuits, whichare well known in the art, and therefore, will not be described anyfurther.

The processing system 2010 is coupled to a transceiver 2040. Thetransceiver 2040 is coupled to one or more antennas 2050. Thetransceiver 2040 provides a means for communicating with various otherapparatus over a transmission medium. The processing system 2010includes a processor 2024 coupled to a computer-readable medium 2026.The processor 2024 is responsible for general processing, including theexecution of software stored on the computer-readable medium 2026. Thesoftware, when executed by the processor 2024, causes the processingsystem 2010 to perform the various functions described supra for anyparticular apparatus. The computer-readable medium 2026 may also be usedfor storing data that is manipulated by the processor 2024 whenexecuting software. The processing system further includes modules 2020and 2022. The modules may be software modules running in the processor2024, resident/stored in the computer readable medium 2026, one or morehardware modules coupled to the processor 2024, or some combinationthereof. The processing system 2010 may be a component of the UE 650 andmay include the memory 660 and/or at least one of the TX processor 668,the RX processor 656, and the controller/processor 659.

It is understood that the specific order or hierarchy of steps in theprocesses disclosed is an illustration of exemplary approaches. Basedupon design preferences, it is understood that the specific order orhierarchy of steps in the processes may be rearranged. The accompanyingmethod claims present elements of the various steps in a sample order,and are not meant to be limited to the specific order or hierarchypresented.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. §112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

What is claimed is:
 1. A method for wireless communications by a basestation (BS), the method comprising: determining a map, the mapcorrelating channel state information reference signal (CSI-RS)resources with a CSI feedback report request based, at least in part, onthe timing of the request; determining a set of one or more referenceCSI-RS resources for feedback reporting; transmitting a request for aCSI feedback report at a time, based at least in part on a mapping ofthe set of one or more reference CSI-RS resources to the time; receivinga feedback report based on the set of one or more reference CSI-RSresources.
 2. The method of claim 1, wherein the set of one or morereference CSI-RS resources comprises a predetermined number of CSI-RSresources, wherein the predetermined number is signaled to a UE.
 3. Themethod of claim 1, wherein: CSI-RS resources have a one-to-oneassociation with subframe sets; and the set of one or more referenceCSI-RS resources comprises CSI-RS resources whose subframe set containsthe subframe in which the request is sent.
 4. The method of claim 3,further comprising transmitting signaling including a bitmap, the bitmapindicating the subframe sets.
 5. The method of claim 1, wherein the setof one or more reference CSI-RS resources comprises multipleCSI-resources contained in a single subframe.
 6. The method of claim 5,wherein the feedback report is based on a CSI-RS resource subset, theCSI-RS resource subset having less than all CSI-RS resources containedin the one subframe.
 7. The method of claim 6, further comprisingtransmitting signaling indicating the CSI-RS resource subset.
 8. Anapparatus for wireless communications, comprising: at least oneprocessor configured to: determine a map, the map correlating channelstate information reference signal (CSI-RS) resources with a CSIfeedback report request based, at least in part, on the timing of therequest; and determine a set of one or more reference CSI-RS resourcesfor feedback reporting; a transmitter configured to: transmit a requestfor a CSI feedback report at a time, based at least in part on a mappingof the set of one or more reference CSI-RS resources to the time; and areceiver configured to: receive a feedback report based on the set ofone or more reference CSI-RS resources.
 9. The apparatus of claim 8,wherein the set of one or more reference CSI-RS resources comprises apredetermined number of CSI-RS resources, wherein the predeterminednumber is signaled to a UE.
 10. The apparatus of claim 8, wherein:CSI-RS resources have a one-to-one association with subframe sets; andthe set of one or more reference CSI-RS resources comprises CSI-RSresources whose subframe set contains the subframe in which the requestis sent.
 11. The apparatus of claim 10, further comprising transmittingsignaling including a bitmap, the bitmap indicating the subframe sets.12. The apparatus of claim 8, wherein the set of one or more referenceCSI-RS resources comprises multiple CSI-resources contained in a singlesubframe.
 13. The apparatus of claim 12, wherein the feedback report isbased on a CSI-RS resource subset, the CSI-RS resource subset havingless than all CSI-RS resources contained in the one subframe.
 14. Theapparatus of claim 13, further comprising transmitting signalingindicating the CSI-RS resource subset.
 15. An apparatus for wirelesscommunications, comprising: means for determining a map, the mapcorrelating channel state information reference signal (CSI-RS)resources with a CSI feedback report request based, at least in part, onthe timing of the request; means for determining a set of one or morereference CSI-RS resources for feedback reporting; means fortransmitting a request for a CSI feedback report at a time, based atleast in part on a mapping of the set of one or more reference CSI-RSresources to the time; means for receiving a feedback report based onthe set of one or more reference CSI-RS resources.
 16. The apparatus ofclaim 15, wherein the set of one or more reference CSI-RS resourcescomprises a predetermined number of CSI-RS resources, wherein thepredetermined number is signaled to a UE.
 17. The apparatus of claim 15,wherein: CSI-RS resources have a one-to-one association with subframesets; and the set of one or more reference CSI-RS resources comprisesCSI-RS resources whose subframe set contains the subframe in which therequest is sent.
 18. The apparatus of claim 17, further comprising meansfor transmitting signaling including a bitmap, the bitmap indicating thesubframe sets.
 19. The apparatus of claim 15, wherein the set of one ormore reference CSI-RS resources comprises multiple CSI-resourcescontained in a single subframe.
 20. The apparatus of claim 19, whereinthe feedback report is based on a CSI-RS resource subset, the CSI-RSresource subset having less than all CSI-RS resources contained in theone subframe.
 21. The apparatus of claim 20, further comprising meansfor transmitting signaling indicating the CSI-RS resource subset.
 22. Acomputer-readable medium having encoded thereon program code forwireless communications, the program code being executed by a processorand comprising: program code to determine a map, the map correlatingchannel state information reference signal (CSI-RS) resources with a CSIfeedback report request based, at least in part, on the timing of therequest; program code to determine a set of one or more reference CSI-RSresources for feedback reporting; program code to transmit a request fora CSI feedback report at a time, based at least in part on a mapping ofthe set of one or more reference CSI-RS resources to the time; programcode to receive a feedback report based on the set of one or morereference CSI-RS resources.